The human brain is an exceedingly delicate structure protected by a series of envelopes to shield it from injury. The innermost layer, the pia mater, covers the surface of the brain. Next to the pia mater is the arachnoid layer, a spidery web-like membrane that acts like a waterproof membrane. Finally, the dura mater, a tough leather like layer, covers the arachnoid layer and adheres to the bones of the skull.
While this structure protects against penetrating trauma because of the bones of the skull, the softer inner layers absorb too little energy before the force is transmitted to the brain itself. Additionally, while the skull may dampen some of the linear force applied to the head, it does nothing to mitigate the effects of angular forces that impart rotational spin to the head. Many surgeons in the field believe the angular or rotational forces applied to the brain are more hazardous than direct linear forces due to the twisting or shear forces they apply to the white matter tracts and the brain stem itself. In addition, because the person's head and the colliding object (including another person's head) are moving independently and in different angles, angular forces, as well as linear forces, are almost always involved in head injuries.
Mild traumatic brain injury (MTBI), more commonly known as “concussion,” is a type of brain injury that occurs frequently in many settings such as construction worksites, manufacturing sites, and athletic endeavors and is particularly problematic in contact sports. While at one time concussion was viewed as a trivial and reversible brain injury, it has become apparent that repetitive concussions, even without loss of consciousness, are serious deleterious events that contribute to debilitating disease processes such as dementia and neuro-degenerative diseases for example Parkinson's disease, chronic traumatic encephalopathy (CTE), and pugilistic dementias.
U.S. Pat. No. 5,815,846 by Calonge describes a helmet with fluid filled chambers that dissipate force by squeezing fluid into adjacent equalization pockets when external force is applied. In such a scenario, energy is dissipated only through viscous friction as fluid is restrictively transferred from one pocket to another. Energy dissipation in this scenario is inversely proportional to the size of the hole between the full pocket and the empty pocket. That is to say, the smaller the hole, the greater the energy drop. The problem with this design is that, as the size of the hole is decreased and the energy dissipation increases, the time to dissipate the energy also increases. Because fluid filled chambers react hydraulically, energy transfer is in essence instantaneous, hence, in the Calonge design, substantial energy is transferred to the brain before viscous fluid can be displaced negating a large portion of the protective function provided by the fluid filled chambers. Viscous friction is too slow an energy dissipating modification to adequately mitigate concussive force. If one were to displace water from a squeeze bottle one can get an idea as to the function of time and force required to displace any fluid when the size of the exit hole is varied. The smaller the transit hole, the greater the force required and the longer the time required for any given force to displace fluid.
U.S. Pat. No. 3,872,511 to Nichols discloses a helmet with hard inner and outer shells with an intermediate zone between the two shells. The zone contains a plurality of fluid-filled bladders that are held to the inner surface of the outer shell by means of a valve. When an impact occurs the outer shell is forced into the zone squeezing the bladders. The valve closes upon impact causing the air to be retained in the bladders to cushion the impact from the user's head. However, because the movement of the bladders is restricted at impact, the force of the impact, although reduced is still directed into the head. In addition, the '511 patent makes no provision for mitigation of rotational forces striking the helmet.
U.S. Pat. No. 6,658,671 to Holst discloses a helmet with an inner and outer shell with a sliding layer in between. The sliding layer allows for the displacement of the outer shell relative to the inner shell to help dissipate some of the angular force during a collision applied to the helmet. However, the force dissipation is confined to the outer shell of the helmet. In addition, the Holst helmet provides no mechanism to return the two shells to the resting position relative to each other. A similar shortcoming is seen in the helmet disclosed in U.S. Pat. No. 5,596,777 to Popovich and European patent publication EP 0048442 to Kalman, et al.
German Patent DE 19544375 to Zhan discloses a construction helmet that includes apertures in the hard outer shell that allows the expansion of what appears to be a foam inner liner through the apertures to dispel some of the force of a collision. However, because the inner liner appears to rest against the user's head, some force will be directed toward rather than away from the head. In addition, there is no mechanism to return the expanded foam liner back to the inside of the helmet.
U.S. Patent Application Publication No. 2012/0198604 to Weber, et al. discloses a safety helmet for protecting the human head against repetitive impacts as well as moderate and sever impacts to reduce the likelihood of brain injury caused by both translational and rotational forces. The helmet includes isolation dampers that act to separate an outer liner from an inner liner. Gaps are provided between the ends of the outer liner and the inner liner to provide space to enable the outer liner to move without contacting the inner liner upon impact. However, it appears that several layers of isolation dampers and outer liners are necessary and no effective protection is provided to protect the brain from direct translational blows.
Clearly to prevent traumatic brain injury, not only must penetrating objects be stopped, but any force, angular or linear, imparted to the exterior of the helmet must also be prevented from simply being transmitted to the enclosed skull and brain. That is to say that the helmet must not merely play a passive role in dampening such external forces, but must play an active role in dissipating or misdirecting both linear and angular momentum imparted by said threes such that they have little or no deleterious effect on the delicate brain.
To achieve these ends one must conceive of the helmet much as biologic evolution has of the skull and the brain. That is to say, to afford maximal protection from linear and angular forces, the skull and the brain must be capable of movement independent of each other, and to have mechanisms which dissipate imparted kinetic energy, regardless of the vector or vectors by which it is applied.
To attain these objectives in a helmet design, the inner component (shell) and the outer component (shell or shells) must be capable of appreciable degrees of movement independent of each other. Additionally, the momentum imparted to the outer shell should both be directed away from and/or around the underlying inner shell and brain and sufficiently dissipated so as to negate deleterious effects.
Another difficulty with protective helmets is the tight fit of the helmet against the user's head. To fit properly, the narrow opening of a conventional helmet must be pulled over the widest part of the user's head Often the fit is so snug that it can be painful to pull the helmet over the user's head and protruding ears. Consequently, a user may use a larger helmet, which while more comfortable and easier to put on, does not provide the level of protection obtainable with a correctly fitted helmet.
Clearly, there is a need in the art and science of protective head gear design to mitigate these deleterious consequences of repetitive traumatic brain injury. There is also a need in the field for a helmet that can provide the protection achieved with a proper fit and still be relatively easy to pull over a user's head.